Sensor Resistance Testing; Sensor Resistance At Various Temperatures - andrews 24/39 Installation And Service Manual

10 Appendix
Fig. 85
Upper thermistor
location (applicable
models)
Lower thermistor
access located
inside control box.
Are readings correct
Yes
Check harness
continuity.
continuity okay?
Yes
Replace control board
°C 0 1
4.5 26109 25400
10 19906 19383
15.5 15314 14925
21.1 11884 11592
26.7 9299 9078
32 7333 7165
37 5827 5697
44 4663 4562
49 3758 3679
55 3048 2986
60 2488 2439
65.5 2043 2004
71 1688 1656
76 1402 1376
82 1170 1150
88 982 965
93 828 814
94
No
Replace thermistor
No
Replace harness
In Degrees C
2 3
24712 24045 23399
18876 18383 17905
14548 14180 13823
11308 11032 10763
8862 8653 8449
7000 6839 6683
5570 5446 5326
4464 4368 4274
3602 3527 3453
2925 2866 2808
2391 2344 2298
1966 1928 1891
1625 1595 1566
1351 1327 1303
1129 1110 1090
949 933 917
801 788 775

10.5.2 Sensor resistance testing

Upper Sensor
1. Determine resistance value of upper sensor. Test across
grey wires.
2. Draw quart of water off T&P valve. Using a thermometer,
determine water temperature.
3. Use table below to verify correct resistance per water
temperature measured.
Lower Sensor:
1. Determine resistance value of lower sensor. Test across
center wire (common) to each outside wire. Resistance of
both thermistors in the lower sensor should be close to each
other. If the resistance values for both thermistors are not
close to each other, replace the lower sensor. The dual
thermistors are used to provide high limit protection in case
the thermostat circuit fails to shut off the water heater.
2. Draw quart of water off Drain Valve. Using a thermometer,
determine water temperature.
3. Use table below to verify correct resistance per water
temperature measured.
Caution
Be Careful When Making Resistance Measurements Not
to Damage or Deform Connectors or Connector Pins.

10.5.3 Sensor resistance at various temperatures

Example: If water temperature is 26.7°C, then the resistance
through the sensor would be 8449 (see shaded area).
Note
Sensor resistance increases as the temperature falls.
4 5 6
22771 22163
17440 16990
13477 13140
10502 10248
8250 8057
6531 6383
5208 5094
4183 4094
3382 3312
2752 2697
2253 2209
1856 1820
1537 1509
1280 1257
1071 1053
901 886
762 749
7 8 9
21573 21000 20445
16553 16128 15715
12812 12494 12185
1000 9760 9526
7869 7685 7507
6238 6098 5961
4982 4873 4767
4006 3922 3839
3244 3177 3112
2643 2590 2538
2166 2124 2083
1786 1753 1720
1481 1454 1427
1235 1213 1191
1035 1017 999
871 857 842
737 725 713
Issue 2 14/07/16